When playing a video on a device, such as a mobile device, a user may scrub a timeline, such as by holding and dragging his/her finger across a content playback timeline. In scrubbing the timeline, the user moves his/her finger to a different position (e.g., time) than the current time in the video being played. The device tracks the user's finger and displays a user interface widget, which may include a progress indicator, that shows the content time offset corresponding to the position in which the user has dragged his/her finger. The user interface widget also contains a space for a preview image. The device can decide to fetch and display a preview image within the user interface widget. To fetch the image, the device transmits a current content identifier and a time offset corresponding to the position of the user's finger to a server. The server then responds with an image for that time offset. If the user moves his/her finger to multiple positions on the timeline, the device may send many requests for images to the server. Each image request may take a significant amount of time due to network connection latency, especially with multiple requests competing for bandwidth.